In vehicles, power consumption of electric loads such as indicators, blinkers, blowers, wipers, and air conditioners are typically supplied from a battery. An alternator as an AC generator is driven by driving force from an engine to generate electric power to charge the battery.
The alternator is connected to an engine side through a belt entrained around a crank pulley of a crankshaft of an engine, and is driven by rotation of the crankshaft to generate power. To restrain or cover the variation in the electric load including the battery, the current passing through a field coil (primary field coil) is changed according to the voltage fluctuations. By this configuration, inside of the alternator, the power generation current is self-changed to achieve a power supply to the system without discharge of the battery.
However, the alternator imposes a corresponding load on the engine. Engine control by the usual increase in idle air quantity (ISC control) cannot sufficiently cover the quick electric load variations. This results in hunting or reduces engine speed, and may cause the engine to stall if the worst happens.
While the battery supplies power to cover the load which could not be dealt with by the alternator, the battery is soon charged by the alternator under control of a regulator circuit. With usual control of the alternator, there is no allowance for the battery to receive regenerative current during deceleration of the vehicle, which is disadvantageous in that the deceleration energy is not effectively utilized.
To obviate these inconveniences, the three following methods are usually provided.
In a first control method, prevention of the power generation of the alternator (i.e., power generation cut or alternator-cut) is generally employed. By controlling a terminal C (switch for switching the voltage of the alternator), the alternator decreases in voltage output and is prevented from power generation (actually the power generation is reduced). A second control method is an FR (or FD; field duty) direct control to directly control the alternator by the signal from a controller (engine controller; ECM) to the field coil (primary coil) itself. A third control method is an FR duty control (or field current duty (FD) control) to change a duty ratio of a rectangular-wave current generated by the regulator circuit built in the alternator so as to cover the variation in requirement of the load including the battery. Decision of the timing of power generation cut of the alternator determines the duration of the power generation cut in accordance with the voltage, which is detected as a duty ratio so that a state of the battery can be detected. Alternatively, these methods can be appropriately combined to deal with the problem.
In view of that, the generator in operation becomes a mechanical load on the engine, some of these power generation controllers for the vehicle control a field current, which controls the operation of the generator, with a certain pattern to cover the variation in the mechanical load on the engine (see JP-2528995).
In a conventional power generation controller for the alternator of the first method in which power generation cut (charge cut) of the alternator is executed, a torque required for the engine varies largely when canceling the power generation cut by the terminal C. To avoid this variation in torque, it is generally required that the alternator generates power gradually (by gradual excitation). Particularly, this gradual excitation is required during an idle speed operating condition where only low engine power can be output. However, the loads vary continuously so that an idle speed controller cannot learn an idle air quantity, thereby limiting engine startup.
With the second FR direct control method, it is required to detect states of the battery and the loads, which are generally detected by usual methods, by another method so as to directly control the alternator. For example, the states of the battery and the loads can be detected, since the voltage decreases when variation in the electric loads occurs. However, the states thereof cannot be detected while vehicle speed is increasing, since the capacity of the alternator increases with increase in the engine speed and the variation in the electric loads becomes small. It is therefore difficult to determine the exact status.
Further, with the third control method, the FR duty control is performed in combination with the first control, namely the power generation cut of the alternator. If the alternator is prevented from power generating (charge cut) by the terminal C, the condition of the battery can be detected due to the battery being in a discharge state without the electric loads. But this can be applied only under a constant electric load, since combinations of the electric loads and the states of the battery effect this determination. Also, if the alternator is not prevented from power generating by the terminal C, it cannot be determined from FD (field duty) whether FD is generated only for electric load, or in addition to this, for charging the battery. Therefore, switches are undesirably required to determine the electric loads to ensure protection of the battery.
In the power generation controller for the alternator, there is also a problem in which the alternator requires the engine to produce relatively large torque during idle speed operation where the engine speed is low, thereby deteriorating stability of the idle speed operation. By increasing intake air at idle speed (ISC; idle speed control), the engine speed can often be increased to deal with the electric loads. However, abuse of this increase deteriorates fuel economy.
Further, in the power generation controller for the alternator, current through the field coil (primary coil) of the alternator is changed according to a duty ratio of rectangular-wave current generated from the built-in regulator circuit so as to cover the variation in load requirements. Power generation starts when the speed of the internal combustion engine cranked by a starter at engine startup exceeds speed for minimum power generation current, which deteriorates startability. This is because the alternator is self-controlled. An additional function is desired to prevent the power generation at engine startup.
During idle speed operation in which the engine speed is low, the alternator requires relatively large engine torque, thereby deteriorating stability of the idle speed operation. There is often an undesirable increase of the idle engine speed when the duty ratio of current through the field coil (primary coil) is increased for the electric load.
Still further, the battery provides power to the electric load that is not covered by the alternator. The battery is soon charged by the control of the regulator circuit of the alternator. Accordingly, there is no allowance for the battery to receive regenerative current during deceleration of the vehicle, which is disadvantageous in that the deceleration energy is not effectively utilized.